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10.4: Fix full-speed fan issue with 10.4.4 on iMac G5s
Authored by: ballardmac on Jan 17, '06 11:24:27PM

Yes, mm2270 is pretty much right on. Recent versions of the PMG5 & IMG5 (ALS) have an advanced SMU instead of a PMU, but it serves a similar purpose.

The SMU controls the fans and regulates the speeds to run each fan. The SMU derives fan speed from sensors in each thermal zone. Some of these sensors monitor thermal only, while others monitor both thermal and power.

If the SMU does not receive an update from the operating system within two minutes, it begins to ramp up the speed of the fans to full speed. This is sort of a self-preservation function.

Follow previous steps (in previous post) to reset SMU. Remember that your date and time will be reset, unless you have enabled "Set date & time automatically" in System Preferences.

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